fix(audio): Campaign A slice A1 — retail's sound probability gate (#355)

The SoundTable probability field is a Bernoulli play/skip gate applied at
the play site (SoundManager::PlayProbability @0x005500E0), not a selection
weight — and variant selection (SoundManager::GetSound @0x00550680) is a
uniform index over (n-1) that ignores probability entirely. SoundCookbook
did the opposite: a cumulative-distribution walk weighted BY probability,
short-circuiting single-entry lists before rolling at all.

A dat census says 4,183 of 4,184 entries are single-entry and 686 of those
carry probability < 1.0, so the gate was categorically absent: Speak1 idle
chatter authored at 0.05 fired every trigger (~20x too often), wound/attack/
swoosh variants never dropped, and six 0.0001 entries always played.

Split into retail's two steps (PickVariant + PlayProbability, composed by
Select) over a new ISoundRandom modelling both retail roll ranges: the
variant roll clamped below 1.0 (0x00797D48) and the gate's 1/32767 grid,
which is why 0.0001 resolves to ~1.2e-4. PickVariant reproduces retail's
(n-1) off-by-one verbatim per the port-faithfully rule — the last variant
of a multi-entry sound is unreachable, costing exactly one wave
(0x0A00051E) in the shipped dats.

Also removes invented mechanism this review disproved: the dead Core
SoundEntry/ISoundCache scaffold (PitchMin/PitchMax, Loop, Is3D — retail
never calls SetFrequency, never sets the loop flag, and creates every
gameplay buffer 2D), the engine's pitch plumbing, the int 0..7 priority
cast (the dat field is a float in [0,1]; 4,100 entries collapsed to 0),
and the clamp-at-the-field on volume (an unbounded gain retail clamps only
after the distance divide).

Tests rewritten as conformance against the disassembled values, replacing
a self-referential suite that pinned the wrong model.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/AcDream.App/Audio/OpenAlAudioEngine.cs

@@ -80,7 +80,11 @@ public sealed unsafe class OpenAlAudioEngine : IAudioEngine, IWorldAudioQuiescen
         public uint OwnerId;
         public float PlayingGain; // gain at play time (for eviction compare)
         public bool InUse;
-        public uint PriorityBase; // raw priority from SoundEntry.Priority
+        // The DAT-authored priority, a float in [0,1] — NOT an 0..7 int. 4,100
+        // of the shipped entries carry a sub-1.0 priority that an int cast
+        // collapsed to 0, which flattened the eviction ordering this field
+        // exists for. A2 makes eviction compare it.
+        public float Priority;
     }
     private readonly Slot3D[] _pool3D = CreateWorldSlots();
     private int _pool3DCursor; // round-robin start
@@ -251,8 +255,7 @@ public sealed unsafe class OpenAlAudioEngine : IAudioEngine, IWorldAudioQuiescen
         WaveData wave,
         Vector3 position,
         float volume,
-        float priority,
-        float pitch = 1.0f)
+        float priority)
     {
         if (_worldAudioSuspended || !_available || _al is null) return false;
 
@@ -285,7 +288,8 @@ public sealed unsafe class OpenAlAudioEngine : IAudioEngine, IWorldAudioQuiescen
         _al.SetSourceProperty(slot.SourceId, SourceInteger.Buffer, 0);  // detach old
         _al.SetSourceProperty(slot.SourceId, SourceInteger.Buffer, (int)buffer);
         _al.SetSourceProperty(slot.SourceId, SourceFloat.Gain, effectiveGain);
-        _al.SetSourceProperty(slot.SourceId, SourceFloat.Pitch, pitch);
+        // No pitch: retail never calls SetFrequency on a sound buffer, so
+        // there is no per-play pitch variation to reproduce.
         _al.SetSourceProperty(slot.SourceId, SourceVector3.Position, position.X, position.Y, position.Z);
         _al.SetSourceProperty(slot.SourceId, SourceBoolean.SourceRelative, false);
         _al.SetSourceProperty(slot.SourceId, SourceBoolean.Looping, false);
@@ -294,7 +298,7 @@ public sealed unsafe class OpenAlAudioEngine : IAudioEngine, IWorldAudioQuiescen
         slot.PlayingGain = effectiveGain;
         slot.InUse = true;
         slot.OwnerId = ownerId;
-        slot.PriorityBase = (uint)Math.Clamp((int)priority, 0, 7);
+        slot.Priority = priority;
         _pool3DCursor = (slotIdx + 1) & (PoolSize3D - 1);
         return true;
     }
@@ -330,7 +334,7 @@ public sealed unsafe class OpenAlAudioEngine : IAudioEngine, IWorldAudioQuiescen
     /// Play a raw WaveData blob as a 2D UI sound (no falloff, ignores
     /// listener position).
     /// </summary>
-    public bool PlayUiWave(uint waveId, WaveData wave, float volume = 1f, float pitch = 1f)
+    public bool PlayUiWave(uint waveId, WaveData wave, float volume = 1f)
     {
         if (!_available || _al is null) return false;
 
@@ -350,7 +354,6 @@ public sealed unsafe class OpenAlAudioEngine : IAudioEngine, IWorldAudioQuiescen
         _al.SetSourceProperty(src, SourceInteger.Buffer, 0);
         _al.SetSourceProperty(src, SourceInteger.Buffer, (int)buffer);
         _al.SetSourceProperty(src, SourceFloat.Gain, Math.Clamp(volume, 0f, 1f) * SfxVolume);
-        _al.SetSourceProperty(src, SourceFloat.Pitch, pitch);
         _al.SourcePlay(src);
         return true;
     }
@@ -517,7 +520,7 @@ public sealed unsafe class OpenAlAudioEngine : IAudioEngine, IWorldAudioQuiescen
 
         slot.OwnerId = 0;
         slot.PlayingGain = 0f;
-        slot.PriorityBase = 0;
+        slot.Priority = 0f;
         slot.InUse = false;
     }